1. Field of the Invention
The present invention relates to a display apparatus and a control method thereof. More particularly, the present invention relates to a display apparatus, which improves image quality by reducing the time required to increase/decrease an amount of current supplied to a light source, and a control method thereof.
2. Description of the Related Art
A display apparatus such as a liquid crystal display (LCD) or a digital lighting processing (DLP) device employs a light emitting diode (LED) as a light source of a backlight unit. The LED is a point light source that provides high brightness and excellent color realization. Also, the LED is mercury-free and thus eco-friendly. The light emitting device such as the LED is driven by a current. Ideally, the light emitting device requires a driver having an output current with minimized ripples and with a quick response speed to improve image quality.
A conventional display apparatus having such an LED light source is classified as either a linear type or a switching type according to the control method of the LED light source. The switching type is not affected by load resistance, operates stably and is easily structured, compared to the linear type. Hereinafter, a control method of the LED light source using the conventional switching type will be described with reference to FIG. 1.
As shown therein, a current having a value of “ia” flows to the LED light source in a PWM on period (t1-t3, t5-) to turn on the LED light source. The current does not flow to the LED light source in a PWM off period (t3-t5) so that the LED light source is turned off. A switch is switched on and off in the PWM on period (t1-t3, t5-) according to a size of the necessary power for the LED light source, thereby increasing/decreasing the amount of the current supplied to the LED light source and allowing a current having the average value of “ia” flowing therein over the time t2-t3.
When the conventional switching type display apparatus is used, it takes times T1 and T3 for the current flowing in the LED light source to reach the average current value “ia” from the time t1 and t5 of the PWM on period, respectively, thereby causing a slow response speed. When reaching the time t3, which begins the PWM off period, it takes time T2 to consume an energy charged in an inductor and a capacitor through the LED light source, also causing a slow response speed.
The conventional display apparatus having the switching type control for the LED light source also has a limitation regarding a ripple supplied to the LED. Furthermore, the conventional display apparatus is limited with regard to a response speed to maintain image quality when the LED light source is turned on/off or a current used to drive the LED light source is changed.
Accordingly, there is a need for an improved display apparatus and control method thereof having an improved response speed and quality.